1. Field of the Invention
The present invention relates to a method for testing visual capacity and, more particularly, to such a method which is particularly well suited to determining, on an objective basis, the visual acuity of a test subject for a multiplicity of different purposes.
2. Description of the Prior Art
It has long been known that the visual capacity of human beings, as well as animals and other living creatures, is of significance in a variety of different respects. A determination in this regard may be useful for a multiplicity of different purposes. For example, the visual acuity of a test subject may be of importance in itself, or may be indicative of other physical conditions, capabilities, potential capabilities, and the like. For hundreds of years, it has been known to test the visual acuity of human beings and, based upon the determinations made during the tests, to provide corrective means for improving the visual acuity of the people who were the subjects of the tests. Over the centuries, both the reliability of the tests and the capability for providing correction have, in general, improved.
However, it has similarly long been recognized that the reliability of such tests is influenced by a host of different factors not directly related to the actual visual acuity of the test subject. For example, the tests themselves may inherently be unreliable. The tests may be subject to influence, or the introduction of error, by the person conducting the test. The test subject may be influenced in one way or another to endeavor to distort the test results to indicate greater or lesser visual acuity. Other physical conditions of the test subject may have a bearing, or may otherwise influence, the test results. For example, where neurological or emotional disorders exist in the test subject, the test results may be influenced. The test subject may be too young or too old, or may not have adequate language skills to be able to communicate sufficiently well for reliable results to be obtained. In other cases, the test subject may be other than a human being, such as where the test subject is an animal. All of these and many other circumstances may cause prior art visual tests to be compromised to the extent that the results are partially, or wholly, unreliable.
For these and other reasons, it has long been recognized that the creation of an objective test for the visual capacity of a test subject would, in most respects, have significantly more value than the prior art subjective tests which may be compromised by all of the deficiencies heretofore set forth. Thus, for example, the work of Purkinje and of von Helmholtz in the nineteenth century and of others noted the value of such objective tests for visual capacity. More specifically, it has previously been recognized that an objective physical response identified scientifically as "reflex optokinetic nystagmus" is an involuntary reaction to certain stimuli, including visual stimuli. This reaction occurs in all human beings, as well as in animals, and other living creatures. One example of a common environmental circumstance in which this involuntary physical response occurs is where the field of vision of the subject is intersected by a plurality of visual targets moving at a rate of speed through the field of vision which involuntarily causes the eyes to detect and follow one of the visual targets. The eyes involuntarily follow the selected visual target and, upon that target moving sufficiently laterally within the field of vision, the eyes involuntarily travel in a return direction and detect and follow a succeeding visual target until that visual target, in turn, reaches the lateral edge of the field of vision. This process is repeated continuously for as long as the focus of attention is on the visual targets. A common specific example of this phenomenon is the involuntary reaction of the eyes watching telephone poles being passed while traveling in an automobile or a train, for example.
The physiological explanation for the existence of reflex optokinetic nystagmus involves the mechanisms designed to move the directional axes of the eyes to align the most discriminatory receptor elements, or more specifically the cones of the fovea, with whatever is being visualized, or may need to be visualized. These motions of alignment involve the rotary muscles of each eye, synchronized with its fellow eye, as well as the eyelids, the neck, the shoulders and the entire body of the subject, if the circumstances evoke such a response. Most of these motor functions are normally voluntary, but when involved as a defense mechanism they are involuntary and thus unavoidable.
For example, an unexpected sound or glimpse of an object laterally within the field of vision will cause a rapid reflex turning to the side at which the stimulus is detected. The eyes turn to the limit of visibility in that direction. The eyelids lift for full and unobstructed vision. The neck turns in that direction, as do the shoulders, and, if necessary, the trunk, the legs and the feet of the subject. This same basic response occurs in animals and other living creatures. The apparent biological purpose for this physical response is for the creature to detect and face a possible danger and to afford the optimum visualization of that danger. To reiterate, these responses are involuntary in the circumstances described.
Another physiological consideration having a bearing upon the subject invention is "visual acuity." Visual acuity refers to the ability of an eye to resolve details of form. This is generally measured as the minimal angular separation, in fractions of minutes, of two lines which are just resolvable by the eye as separate. Prior art devices, which have been dependent upon these physiological mechanisms, include the Snellen type visual acuity device. Other typical examples of such a prior art devices include a cylinder which is inscribed with stripes. In use, the device is rotated in the field of vision of the test subject to cause reflex optokinetic nystagmus to occur. A wide variety of other types of devices have also been developed. They are, typically, clumsy and unreliable hand held devices, or complex and expensive mechanical devices. In both cases, such prior art devices are so deficient as to be largely without significant practical value.
Therefore, it has long been known that it would be desirable to have a method for testing visual capacity which reliably permits the objective testing of a test subject; which has application to human beings, animals and other forms of life; which achieves a degree of reliability significantly enhanced over that heretofore achieved in the art; which can be employed for the purpose of directly testing the visual acuity of the test subject as well as testing for a multiplicity of other physical conditions that may be evidenced, or otherwise evaluated, based on the visual acuity of the test subject; which can be employed, more generally, in a multiplicity of environments wherein it is desirable, or of importance, to know what the visual acuity is of the test subject without compromise or influence by subjective considerations; which is comparatively inexpensive to employ while being adaptable to virtually all operative environments; and which is otherwise entirely suited to achieving its operational objectives.